This is He Who came by (with) water and blood [ His baptism and His death], Jesus Christ (the Messiah) -- "not by (in) the water only, but by (in) the water and the blood. And it is the [Holy] Spirit Who bears witness, because the [Holy] Spirit is the Truth.

If we accept [as we do] the testimony of men [if we are willing to take human authority], the testimony of God is greater (of stronger authority), for this is the testimony of God, even the witness which He has borne regarding His Son.